The GEC 701A (E4205/B/7) and the Mullard ECR30 are small electrostatically deflected cathode ray tubes with a medium persistence green phosphor. Both were designed for oscilloscope use.
As with most of the CRT's from this period the heater-cathode insulation is not good and the maximum voltage differential between them is limited to 50 Volts. In practice with the cathode at about -800 Volts, the heater would be fed from its own transformer winding.
The a1,a3 voltage is given as 800 Volts and the focus anode a2 would be held at about 135 Volts.
The screen is 69 mm diameter and is curved to withstand the external air pressure.
The base pins are bright and look unused.
The pinch at the right and the electron gun with the X plates on the left.
The end window envelope is 41 mm in diameter, and excluding the B12B base pins is 175 mm long.